The present invention relates to multi-section, screw-type mechanisms movable between extended and retracted positions, and to methods of fabrication thereof. More specifically, the invention is concerned with novel and improved appartus for moving telescopically nested elements between an extended position for use in an intended application, and a retracted position, up to several times less than the fully extended length, depending on the number of telescoping elements employed, for storage and/or transport and to novel methods of fabrication of such apparatus.
Many types of towers are used by both the military and civilian sector to support mobile radio, lighting, and sensor systems, and to provide an emergency reaction capability for such applications as restoring power lines downed by a natural disaster. In general, these structures either consist of segments which are assembled horizontally on the ground and then hoisted to a vertical position, or telescoping sections which are extended vertically using hydraulic or pneumatic power, or various types of winch mechanisms which operate in a manner similar to an extension ladder. The latter technique is most commonly employed on truss-type towers. These are generally very complex and bulky because of the large numbers of individual bolted or welded pieces which form the truss structuring of the mast sections, and because of the extensive cabling and pulleys which must be employed to raise and lower the tower.
Hydraulic and pneumatic systems are generally used with masts composed of telescoping tubular segments. A hydraulic lifting system would normally be incorporated inside the structure as a separate set of fluid-drived, tubular segments. A pneumatic system can simplify the design because the mast segments themselves can be directly inflated to provide extension, assuming the segments fit closely together and are properly sealed to prevent air leakage. In spite of its simplicity, a major drawback of the pneumatic approach is its vulnerability to catastrophic failure caused by the rupture of a seal or a simple puncture of the tube wall. This is of particular concern when the structure is in a hostile military environment, or in a remote location where it might be punctured by small arms fire as the object of vandalism or target practise.
It should also be noted that the foregoing mechanisms do not provide a means of producing a retracting force to lower the tower. Therefore, if gravity is insufficient to pull down the tower segments because of wind loading (which increases the sliding friction between the tower segments) or ice build-up between the segments, the tower cannot be lowered. The method described by this invention eliminates these problems by allowing an equally powerful pull-down (retracting) force to be applied with no additional hardware or system complexity. It is obvious that this feature is a necessity for structures which are intended to operate in orientations other than essentially vertical.
Nested, telescoping structures have also been provided wherein relative axial movement of a plurality of sections is provided by mutually engaged, helical screws. Such structures have generally been limited to relatively small-scale, heavy lifting applications, such as automobile jacks, intended for a range of extension and retraction on the order of 8 to 24 inches, as typefied by those shown in U.S. Pat. Nos. 1,593,217, issued July 20, 1926 to Lucker, and 2,069,012, issued Jan. 26, 1937 to Lynes. The jacks of these patents each include either two or three tubular members having external threads over their entire length engaged with internal threads extending for a portion of the length of the circumferentially adjacent member. The threaded, tubular members are surrounded by non-rotatable, unthreaded, telescoping sections which are axially movable with the threaded members between their relatively extended and retracted positions. Such screwjacks have been largely supplanted for automative use by ratchet-type jacks or, in heavier duty applications, by hydraulic jacks, since modern technology has made these alternatives cheaper and easier to implement for small structures such as a car jack.
It is a principal object of the present invention to provide an axially extensible and retractable mechanism including a plurality of mutually telescoping, threaded members wherein the design is optimised for large-scale applications.
Another object is to provide an axially extensible and retractable structure having a plurality of nested, helically threaded segments wherein no threads are externally exposed in any position of the structure without requiring any elements surrounding the threaded segments.
A further object is to provide a tower or mast structure movable between relatively extended and retracted positions by relative rotation of threadedly engaged members with improved means for effecting electrical connection to a payload supported upon and movable with the structure.
Another object is to provide a novel and improved, vertically extensible and retractable sail boat mast.
Another object is to provide a novel and improved extendable and retractable boom structure which can be positioned at any angle between 0 to 90 degrees.
Still another object is to provide for the use of high strength, low weight materials such as carbon and/or Kevlar reinforced epoxy composites in the fabrication of the above structure.
Other objects will in part be obvious and will in part appear hereinafter.